This invention relates generally to tandem press systems and more specifically to a tandem press system for high speed, flexible manufacture of stator and rotor cores of a dynamoelectric machine.
Competitive mass production of dynamoelectric machines in the form of electric motors, such as those used in household appliances and other machines, requires in the manufacture of the motor an emphasis on speed and continuity of operation. Production of stator and rotor cores of the motors has been carried out in a tandem press arrangement in which a web of highly magnetically permeable stock material is fed to a first (rotor) press and then to a second (stator) press. The rotor press punches out rotor laminations and stacks them in groups to form a rotor core. Similarly, the stator press punches out stator laminations around a central opening left by formation of rotor laminations, and stacks the stator laminations into groups to form a stator core.
Among the obstacles to rapid operation is the introduction of substantial vibrations to the web by virtue of the rapid impact and release of upper die portions of the presses with the web and, in particular, the rapid, intermittent feeding of the web. The vibrations make it difficult to maintain control of the web to the degree necessary to prevent misfeed and accurately punch the web. The problem is particularly acute at the stator press because the web is weakened by removal of material to form rotor laminations in the rotor press. The weakened web bends more easily and tends to become hung up in the stator die.
Continuity of operation is interrupted by the need to connect stock material from a new roll to the web as one roll is used up. Furthermore, to manufacture stator cores for one speed and multiple speed motors, either two separate press systems must be employed, or the stator die must be replaced. Replacement of a die requires a substantial amount of down time for the press.